I had a repeating command block set to this:

execute as @e[type=wither_skull] at @s unless entity @s[type=minecraft:wither_skull,x=-105,dx=59,z=0,dz=59] run say hi 

Any wither skull that is inside this area is supposed to stay silent, and any outside is supposed to say "hi" every tick. This worked for any other entity, and it mostly worked for the wither skull; however, when the skull was summoned by the wither inside that area, the skull said hi once on the first tick of its existence.

I then continued experimenting and made a more complex command block setup to test the NBT one of these skulls for its first 3 ticks. Surprisingly, all 3 ticks had the correct position, so I don't know why it slipped past the command block.

I found this while trying to have a wither area of my creative test world, and I didn't want the skulls to leave the area and destroy other things. When this command is hooked up to a kill command, the wither skulls were killed immediately because of this bug. I understand that this is extremely specific and probably isn't worth it to fix, but it would make this one use case significantly easier.

I also checked, and this does not happen for ghast fireballs.

This is a video showing these things